WASHINGTON (Reuters) - Boeing's troubled Starliner capsule that left two NASA astronauts on the International Space Station last year may need to fly a third uncrewed test flight before it carries astronauts again, agency officials said as the spacecraft's first crew had to return to Earth on a SpaceX capsule this week.

However, before it can secure NASA’s much-anticipated certification for routine flights, the Starliner might need to undertake an additional uncrewed test mission. If required, this would be the fourth such mission, following two uncrewed tests conducted in 2019 and 2022.

The Starliner crew was originally meant to stay on board the ISS for a week, but issues with Boeing's Starliner spacecraft severely delayed their return to Earth.

The two test pilots came to NASA via the Navy. Butch Wilmore, 62, played high school and college football in his home state of Tennessee. Suni Williams, 59, grew up in Needham, Massachusetts, and was a competitive swimmer and distance runner.